From the Test Kitchen

Microwave directions:

In a 1-1/2-quart casserole combine milk, cornstarch, mustard, salt, and pepper. Micro-cook on 100% power (high) for 4 to 6 minutes or until thickened and bubbly, stirring after every minute. Add cheese, stirring until melted. Add ham, broccoli or cauliflower, and mushrooms. Cook 2 to 3 minutes more or until heated through. Serve as directed above.